The small-size power plant based on the ORC process was developed especially for the recovery of waste heat from various heat-producing processes or machines where, due to the temperature of the waste heat or due to the circumstances of the environment, waste heat cannot be used as such or by means of heat exchangers or corresponding means. In a small-size power plant, waste heat is converted generally by a turbine to electricity which is easily used for different purposes.
It can be shown thermodynamically that the Organic Rankine Cycle process is the best applicable method for this kind of energy converting. The heat of vaporization of an organic substance is low in relation to for example, the heat of evaporation of water, and its fall of specific enthalpy in the turbine is small and the mass flow rate in relation to the output is high, and it is possible to reach a high turbine efficiency even in a range of small capacity.
A hermetic or fully closed-circuit process has the advantage that there are no leaks and the process is thus reliable and durable in operation.
The utilization of high-speed technology, wherein the turbine is-directly coupled with a generator rotating at the same speed and thus producing high-frequency current, has made it possible to further simplify the process such that e.g. a separate reduction gear required by conventional processes as well as shaft inlets are not needed.
A hermetic energy converter of this kind, operating on high-speed technology and based on the ORC process, is known from the publication FI-66234, according to which the bearing of the rotor of the high-speed machine is lubricated by an organic circulating medium, wherein the circulating medium is in a gaseous state. Thus it is possible to reach a very high efficiency, because the losses of gaseous bearing are very small. However, for reasons of manufacturing techniques, bearings lubricated with fluid circulating medium have been shown to be more cost-saving.
The use of the circulating medium in a liquid state in the said bearing system is known for example from U.S. Pat. No. 2,961,550 which relates to the bearings of a power plant lubricated by a circulating medium, with special respect to starting up a power plant. According to the publication, the said bearing system is effected by condensating the circulating medium from a gaseous state into a liquid state by a separate condenser, whereafter the fluid circulating medium is directed to the bearings. With particular attention to starting up the power plant, its bearing pipework is equipped with a valve that operates on the basis of the pressure of the circulating medium and opens at an essentially lower pressure than the main valve in the pipework of the primary circulation, wherein the lubrication of bearings starts before the start of the turbine.
In the small-size power plant or energy converter systems in use, a problem has arisen in connection with different stoppage situations due to disturbances, failures and corresponding reasons when the primary circulation to the turbine must be discontinued and the lubrication of the bearings of the rotor in the high-speed machine in the present systems is discontinued or significantly reduced during a stopping situation. Thus the technique used, by which the rotor generally rotates at the synchronous speed of the network (3000 rpm), results in insufficient lubrication which wears down the bearings and essentially reduces their time of use.
The method according to this invention makes it possible to obtain a decisive improvement to the disadvantages presented above and thus to raise the level of technology in the field. To reach this objective, it is characteristic to the method according to this invention that in a stoppage situation of the primary circulation in the main line of the process, the fluid lubrication of the bearings of the rotor is arranged from the vaporizer of the energy converter, such as from a boiler, a process furnace, a ceramic furnace or corresponding, by means of pressurized circulating medium accumulated in the vaporizer.
One of the most important advantages of the method according to the invention is the essentially longer uninterrupted duty cycles of the high-speed machine, and thus also of the entire energy converter, as well as the essentially longer time of use of the bearings of the said rotor. Also, the controllability of the entire process of the energy converter in a stoppage situation is essentially improved.
The following explanation demonstrates the invention in detail and also refers to the attached drawings wherein